Its not unheard of. There's another niche language called "Python" that does exactly the same thing. Comments are `#`, as anyone using a unix shell would expect.
CoffeeScript has always used a single # instead of double // for comments.
In previous versions `//` compiled into an empty regular expression – something a little more difficult to express in JavaScript. But also something pretty much useless — hence the willingness to use it as an operator here.
